Stem cells are cells that can differentiate into various cell types constituting the tissues of an organism, and collectively refer to the cells in an undifferentiated state that can be obtained from embryonic, fetal and adult tissues. The stem cells differentiate into specific cell types under necessary stimulation (environment). Unlike the differentiated cells whose cell division has stopped, they can produce the cells identical to themselves through cell division (self-renewal) and thus can proliferate (expansion). Also, they can differentiate into other cells under different environment or stimulation (plasticity).
Largely, the stem cells are divided into embryonic stem cells (ES cells), which are isolated from the embryo and have the totipotency or pluripotency of differentiating into all cell types, and adult stem cells, which are isolated from the individual cells have multipotency. The inner cell mass during the early embryogenic stage of blastocyte is the mass of cells that will eventually give rise to the structures of the fetus. Theoretically, the embryonic stem cells derived from the inner cell mass have the potential of differentiating into any cell type of the organism. That is to say, the embryonic stem cells are undifferentiated cells that can proliferate infinitely, differentiate into all cell types, and pass their genetic inheritance to the next generation by producing germ cells unlike the adult stem cells.
Human embryonic stem cells are obtained by isolating and culturing the inner cell mass during the formation of human embryo (blastocyst). Currently, the human embryonic stem cells obtained worldwide are derived from the frozen embryos remaining after sterilization. The cells have the totipotency of differentiating into any cell type, can be cultured in immortal, undifferentiated state, and can pass their genetic inheritance to the next generation by producing germ cells (Thomson et al., Science, 282: 1145-1147, 1998; Reubinoff et al., Nat. Biotechnol., 18: 399-404, 2000).
Although various attempts have been made to utilize the human embryonic stem cells capable of differentiating into various cells as cell therapeutic agents, the obstacles of canceration and immune rejection remain to be solved.
Recently, use of mesenchymal stem cells having immunomodulatory function has been proposed to solve these problems. The mesenchymal stem cells are multipotent cells that can differentiate into adipocytes, osteocytes, chondrocytes, myocytes, neurons and cardiomyocytes and are reported to have the immunomodulatory function. Although they can be isolated from various tissues, their abilities differ slightly and surface markers are also different depending on their origin. At present, the mesenchymal stem cells are defined by the ability to differentiate into osteocytes, chondrocytes and myocytes, the spiral shape, and the expression of the surface markers CD73(+), CD105(+), CD34(−) and CD45(−).
The minimum number of cells required for cell therapy or regenerative medicine is around 1×109. Considering the experiments necessary for establishment of conditions and setup of references, the number increases further.
To supply mesenchymal stem cells of various origins in that amount, at least 10 subculturing passages are required in vitro. Then, the cells are no more appropriate for therapy because they become aged and deformed. This is one of the problems of the current system for culturing mesenchymal stem cells. Even when the conditions and references are determined using the cells, the cells may have been depleted already and mesenchymal stem cells from a different person may have to be used. In that case, experiments should be carried out again for the cells. Accordingly, a new method capable of solving these problems is necessary to use the mesenchymal stem cells as cell therapeutic agents.
Korean Patent Publication No. 2005-0032020 discloses adipose-derived stem cells and lattices, and Korean Patent No. 0821128 discloses a method and a system for preparing stem cells from fat tissue.
Throughout the specification, a number of publications and patent documents are referred to and cited. The disclosure of the cited publications and patent documents is incorporated herein by reference in its entirety to more clearly describe the state of the related art and the present disclosure.